Present day integrated circuit processing techniques often employ lithography processing, such as electron beam and X-ray lithography, to write ultra small geometry (submicron line widths) circuitry patterns onto a semiconductor wafer. When two written areas are close together, there may be a cross-dosing of the beam energy (e.g. electrons), causing an (undesirable) increase in size of the adjacent portions of the written areas. This unwanted exposure of a feature by one or more of its neighbors, termed the proximity effect, constitutes the fundamental limit to resolution in lithography processing. The dosage scattering typically extends over a range of several microns, so that virtually all significant wafer features are subject to the effect. Because, in most cases, the effect cannot be eliminated, compensation for scattering must be provided.
Compensation or correction of the proximity effect requires an alteration or modification of the beam dosage based upon area features within a prescribed neighborhood of a feature of interest. Whereas design-rule checking locates regions or features of a pattern that are too close to or not properly aligned with one another, proximity correction is a mechanism by which the pattern is actually corrected based upon a mathematical model of geometrical relationships and scatter. In order to generate the mathematical model it is necessary to locate neighboring features in what is a complex, often multi-element pattern. Computational speed is extremely critical due to the sizes of the data bases involved, and is often limited by the searching mechanism through which the element pattern is analyzed.
Conventional methods of neighbor identification are based upon logical bit-slice operations, where each pixel of a pattern image represents a single bit of data. There is an intrinsic difference, however, between integrated circuit pattern data upon which most design rule checking mechanisms operate and the integrated circuit data used by lithography equipment. The data used by electron beam lithography equipment, for example, is highly `fractured`, being broken into pieces small enough for the machine to physically write with an electron beam, which makes the database intractable by currently employed pattern processing techniques. Proximity checking is especially difficult on highly fractured data, since it is necessary to determine the proximity of all elements of the pattern with respect to each other and involves an extensive two-dimensional search.